/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMeshOverlay.h
Refine an existing overlay topology. For any element on a given triangle, if the predicate returns true, it gets topologically split out so it isn't shared by any other triangle. Used for creating sharp vertices in the normals overlay.
void SplitVerticesWithPredicate ( [TFunctionRef](API\Runtime\Core\GenericPlatform\TFunctionRef)< bool(int ElementIdx, int TriID)> ShouldSplitOutVertex, [TFunctionRef](API\Runtime\Core\GenericPlatform\TFunctionRef)< void(int ElementIdx, int TriID, RealType *FillVect)> GetNewElementValue )